As the electronic device industry was developed, various display devices have been developed, and an image device, a computer, a mobile communication terminal and the like using the same have been developed. A liquid crystal display (LCD) device, which appeared according to this trend, is drawing attention as the display device of a monitor, a mobile communication terminal and the like.
The liquid crystal display (LCD) device is to apply an electrical and optical property of liquid crystal having a middle characteristic of liquid and solid to a display device. Furthermore, the liquid crystal display device is an electric device which converts various kinds of electrical information generated from various devices into visual information using a variation in transmittance of the liquid crystal according to on an applied voltage and transmits the converted visual information. The liquid crystal display device is a flat display device which is being widely used because it has a low operation voltage and electric power consumption and is convenient to carry.
Since the LCD has no self-luminosity to emit light for itself, a backlight is always required for the LCD. The backlight serves as a light source of the LCD. A backlight unit is a composite composed of a light source for radiating light to a rear surface of a liquid crystal module, an electric power circuit for driving the light source, and all components for forming uniform plane light. The backlight unit using a light emitting diode (LED) has been recently suggested as a light source to illuminate the LCD. The LED is a light emitting device which generates light using a light emitting phenomenon generated when a voltage is applied to a semiconductor. The LED has a small size and a long lifespan compared to a conventional light source. Furthermore, it is advantageous that since the LED directly converts electric energy into light energy, it has a low operation voltage at the same time as having high energy efficiency. The backlight unit is used in a state in which a plurality of light emitting devices such as the LED are mounted on a printed circuit board (PCB). Since the printed circuit board should endure heat emitted from the light emitting device, it is mainly formed of a metal material. However, when the heat generated from the light emitting device is not properly emitted, the light emitting device is destroyed or a life span thereof is reduced. Thus, to ensure the heat generated from the light emitting device to be easily emitted, the structure of a metal printed circuit board and the structure of a backlight unit including the same, as described in Korean Patent Laid-Open Publication No. 10-2007-0053517, were suggested.
FIG. 1 simply illustrates a general method of manufacturing a metal printed circuit board as described in aforesaid Korean Patent Laid-Open Publication No. 10-2007-0053517. Referring to FIG. 1, as illustrated in (a) of FIG. 1, an insulating layer 13 and a metal layer 15 are first laminated on an upper front surface of a metal substrate 11 composed of Al or a copper alloy. Furthermore, as illustrate in (b) of FIG. 1, a circuit pattern 16 is formed by patterning the metal layer 15. As illustrated in (c) of FIG. 1, a light emitting device 19 is mounted on the circuit pattern 16. As illustrated in (d) of FIG. 1, an L-shaped metal printed circuit board is formed by bending the metal substrate 11.
However, in the conventional metal printed circuit board having the structure as illustrated in (d) of FIG. 1, as the insulating layer 13 is formed on the front surface of the metal substrate 11, when bending is formed, due to a frangible property (i.e. a brittle property) of the insulating layer itself, a crack is generated at a part P in which the bending is formed. Thus, it is problematic that when a backlight unit is produced using the aforesaid metal printed circuit board, foreign substances generated from the crack of the insulating layer can be entered into an inner part of the backlight unit. Furthermore, as time passes, the crack becomes to grow. Thus, it is problematic that a defect in the circuit pattern can be generated, and that durability and reliability of the backlight unit are reduced.